DESCRIPTION

The
kexec_load()
system call loads a new kernel that can be executed later by
reboot(2).

The
flags
argument is a bit mask that controls the operation of the call.
The following values can be specified in
flags:

KEXEC_ON_CRASH (since Linux 2.6.13)

Execute the new kernel automatically on a system crash.
This "crash kernel" is loaded into an area of reserved memory that
is determined at boot time using the
crashkernel
kernel command-line parameter.
The location of this reserved memory is exported to user space via the
/proc/iomem
file, in an entry labeled "Crash kernel".
A user-space application can parse this file and prepare a list of
segments (see below) that specify this reserved memory as destination.
If this flag is specified, the kernel checks that the
target segments specified in
segments
fall within the reserved region.

KEXEC_PRESERVE_CONTEXT (since Linux 2.6.27)

Preserve the system hardware and
software states before executing the new kernel.
This could be used for system suspend.
This flag is available only if the kernel was configured with
CONFIG_KEXEC_JUMP,
and is effective only if
nr_segments
is greater than 0.

The high-order bits (corresponding to the mask 0xffff0000) of
flags
contain the architecture of the to-be-executed kernel.
Specify (OR) the constant
KEXEC_ARCH_DEFAULT
to use the current architecture,
or one of the following architecture constants
KEXEC_ARCH_386,
KEXEC_ARCH_68K,
KEXEC_ARCH_X86_64,
KEXEC_ARCH_PPC,
KEXEC_ARCH_PPC64,
KEXEC_ARCH_IA_64,
KEXEC_ARCH_ARM,
KEXEC_ARCH_S390,
KEXEC_ARCH_SH,
KEXEC_ARCH_MIPS,
and
KEXEC_ARCH_MIPS_LE.
The architecture must be executable on the CPU of the system.

The
entry
argument is the physical entry address in the kernel image.
The
nr_segments
argument is the number of segments pointed to by the
segments
pointer;
the kernel imposes an (arbitrary) limit of 16 on the number of segments.
The
segments
argument is an array of
kexec_segment
structures which define the kernel layout:

The kernel image defined by
segments
is copied from the calling process into
the kernel either in regular
memory or in reserved memory (if
KEXEC_ON_CRASH
is set).
The kernel first performs various sanity checks on the
information passed in
segments.
If these checks pass, the kernel copies the segment data to kernel memory.
Each segment specified in
segments
is copied as follows:

*

buf
and
bufsz
identify a memory region in the caller's virtual address space
that is the source of the copy.
The value in
bufsz
may not exceed the value in the
memsz
field.

*

mem
and
memsz
specify a physical address range that is the target of the copy.
The values specified in both fields must be multiples of
the system page size.

*

bufsz
bytes are copied from the source buffer to the target kernel buffer.
If
bufsz
is less than
memsz,
then the excess bytes in the kernel buffer are zeroed out.

In case of a normal kexec (i.e., the
KEXEC_ON_CRASH
flag is not set), the segment data is loaded in any available memory
and is moved to the final destination at kexec reboot time (e.g., when the
kexec(8)
command is executed with the
-e
option).

In case of kexec on panic (i.e., the
KEXEC_ON_CRASH
flag is set), the segment data is
loaded to reserved memory at the time of the call, and, after a crash,
the kexec mechanism simply passes control to that kernel.

The
kexec_load()
system call is available only if the kernel was configured with
CONFIG_KEXEC.

kexec_file_load()

The
kexec_file_load()
system call is similar to
kexec_load(),
but it takes a different set of arguments.
It reads the kernel to be loaded from the file referred to by
the file descriptor
kernel_fd,
and the initrd (initial RAM disk)
to be loaded from file referred to by the file descriptor
initrd_fd.
The
cmdline
argument is a pointer to a buffer containing the command line
for the new kernel.
The
cmdline_len
argument specifies size of the buffer.
The last byte in the buffer must be a null byte (aq\0aq).

The
flags
argument is a bit mask which modifies the behavior of the call.
The following values can be specified in
flags:

KEXEC_FILE_UNLOAD

Unload the currently loaded kernel.

KEXEC_FILE_ON_CRASH

Load the new kernel in the memory region reserved for the crash kernel
(as for
KEXEC_ON_CRASH).
This kernel is booted if the currently running kernel crashes.

KEXEC_FILE_NO_INITRAMFS

Loading initrd/initramfs is optional.
Specify this flag if no initramfs is being loaded.
If this flag is set, the value passed in
initrd_fd
is ignored.

The
kexec_file_load()
system call was added to provide support for systems
where "kexec" loading should be restricted to
only kernels that are signed.
This system call is available only if the kernel was configured with
CONFIG_KEXEC_FILE.

RETURN VALUE

On success, these system calls returns 0.
On error, -1 is returned and
errno
is set to indicate the error.

ERRORS

EADDRNOTAVAIL

The
KEXEC_ON_CRASH
flags was specified, but the region specified by the
mem
and
memsz
fields of one of the
segments
entries lies outside the range of memory reserved for the crash kernel.

EADDRNOTAVAIL

The value in a
mem
or
memsz
field in one of the
segments
entries is not a multiple of the system page size.

EBADF

kernel_fd
or
initrd_fd
is not a valid file descriptor.

EBUSY

Another crash kernel is already being loaded
or a crash kernel is already in use.

EINVAL

flags
is invalid.

EINVAL

The value of a
bufsz
field in one of the
segments
entries exceeds the value in the corresponding
memsz
field.

EINVAL

nr_segments
exceeds
KEXEC_SEGMENT_MAX
(16).

EINVAL

Two or more of the kernel target buffers overlap.

EINVAL

The value in
cmdline[cmdline_len-1]
is not aq\0aq.

EINVAL

The file referred to by
kernel_fd
or
initrd_fd
is empty (length zero).

ENOEXEC

kernel_fd
does not refer to an open file, or the kernel can't load this file.
Currently, the file must be a bzImage and contain an x86 kernel that
is loadable above 4 GiB in memory (see the kernel source file
Documentation/x86/boot.txt).

ENOMEM

Could not allocate memory.

EPERM

The caller does not have the
CAP_SYS_BOOT
capability.

VERSIONS

The
kexec_load()
system call first appeared in Linux 2.6.13.
The
kexec_file_load()
system call first appeared in Linux 3.17.

CONFORMING TO

These system calls are Linux-specific.

NOTES

Currently, there is no glibc support for these system calls.
Call them using
syscall(2).

SEE ALSO

COLOPHON

This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
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and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.